Pyridyl sulfonic acids or pyridyl alkyl sulfonic acids as additives to nickel plating baths have been reported. In U.S. Pat. No. 2,839,456, 4-pyridyl ethane sulfonic acid, in combination with other additives, is described as a brightener. Though 2- and 4-pyridine ethane sulfonic acids do improve the luster of deposited nickel layers, they have no influence on their leveling. In U.S. Pat. No. 3,444,056, certain quaternary compounds of pyridine-3-sulfonic acid are mentioned as levelers and brighteners. The N-methyl-pyridine-3-sulfonic acid betaine and N-allyl-pyridine-3-sulfonic acid betaine mentioned in this patent are, however, not fully satisfactory. It appears that nickel deposits turn lusterless and brittle with a too low ampere hour load per liter of nickel bath. This behavior of the bath cannot be prevented by any of the regeneration methods employed in electroplating. The instant compounds of this invention are agents which produce a highly leveled nickel deposit of excellent ductility in a far more constant bath.